Berry-Lovers Must Be Pruners
"Bramble" is the name given to the rubus family of plants, which includes raspberries and blackberries. Even with these hardy plants, pruning reduces the chance of pest invasion and infection, allows better air circulation and light exposure, resulting in more fruit. Pruning most brambles is a necessity simply because they are rampant growers.
Photo provided by the National Gardening Association
How Brambles Grow
It's easier to remember how to prune brambles if you understand how they grow. The plants' underground parts -- the roots and crown -- are perennial, but the canes (upright stems) that grow from the crown live just two years. In its first year, a cane grows vigorously, develops a strong structure, and stores energy. It produces fruit in its second year. After fruiting, the cane declines and dies, though some species called everbearing produce fruit late in their first season and again in their second year.
How and When to Prune Bramble Canes
Since the 2-year old canes die after fruiting, you can cut them back to the ground immediately after harvest. Prune carefully to avoid damaging the bramble's crown with your pruners.
Each category of brambles has a different growth and fruiting habit, so pruning practices vary. At any time of year, you can remove dead, damaged, or diseased branches and canes. If you grow your brambles on trellises, you can leave longer canes.
Pruning Summer-Bearing Red and Golden Raspberries
These brambles produce tall, unbranched canes as well as root suckers. In late winter or early spring before new growth begins, remove canes until there are 8 strong canes per 3 feet of row. If your brambles grow in a bed rather than a row, thin them to 6 to 10 canes per square foot of row. Another way to measure is to leave an average of 4 to 6 inches between canes.
In the early spring as growth is beginning, prune back the tips of second-year canes so they stand erect and about 4 to 5 feet high.
Pruning Black and Purple Raspberries
Unlike their red and golden cousins, black and purple raspberry canes branch vigorously, and grow in a vase shape, producing few if any root suckers. If allowed to grow unpruned, the long canes that come in contact with soil form roots, giving rise to new plants.
In spring, when first-year canes reach 18 to 20 inches tall, prune back the tips. This encourages strong branching. The following spring, trim branches back to 8 to 12 inches. When thinning canes, leave 5 to 10 canes per plant, depending on the soil fertility.
Article provided by the National Gardening Association